Fix run command race (#1470)

* Use exec.CommandContext to simplfy timeout handling

And fixing the data races which can be identified by the added tests when -race enabled.

* Use sleep commmand instead of reading from stdin

* Make the error handling go-esque

modules/process/manager_test.go

@@ -3,6 +3,7 @@ package process
 import (
 	"os/exec"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -31,3 +32,27 @@ func TestManager_Remove(t *testing.T) {
 	_, exists := pm.Processes[pid2]
 	assert.False(t, exists, "PID %d is in the list but shouldn't", pid2)
 }
+
+func TestExecTimeoutNever(t *testing.T) {
+
+	// TODO Investigate how to improve the time elapsed per round.
+	maxLoops := 10
+	for i := 1; i < maxLoops; i++ {
+		_, stderr, err := GetManager().ExecTimeout(5*time.Second, "ExecTimeout", "git", "--version")
+		if err != nil {
+			t.Fatalf("git --version: %v(%s)", err, stderr)
+		}
+	}
+}
+
+func TestExecTimeoutAlways(t *testing.T) {
+
+	maxLoops := 100
+	for i := 1; i < maxLoops; i++ {
+		_, stderr, err := GetManager().ExecTimeout(100*time.Microsecond, "ExecTimeout", "sleep", "5")
+		// TODO Simplify logging and errors to get precise error type. E.g. checking "if err != context.DeadlineExceeded".
+		if err == nil {
+			t.Fatalf("sleep 5 secs: %v(%s)", err, stderr)
+		}
+	}
+}